It is known that a single s.c. injection of testosterone propionate (TP) or estradiol into neonatal female rats during the critical period of brain differentiation is followed post-puberally by a syndrome characterized by anovulation, polycystic ovaries, sterility, and alterations in the normal pattern of female sexual behavior. The nature of the alterations induced in the neonatal brain following steroid administration is unknown, however, these alterations appear to be localized in certain hypothalamic and limbic structures. Several recent studies indicate that the administration of TP to neonatal female rats during the critical period of brain differentiation is followed by alterations in brain nucleic acid and protein synthesis. For example, work from our laboratory has shown that early TP treatment significantly reduced the incorporation of H3-lysine into proteins of specific hypothalamic nuclei, i.e., arcuate, paraventricular, periventricular and supraoptic. The purposes of this quantitative autoradiographic investigation are twofold: 1. To determine if the defects produced by neonatal steroid administration occur as a result of changes induced at the genomic level. 2. To determine if neonatally administered estradiol is followed by alterations in the incorporation of H3-lysine into proteins of specific brain regions.